Strained and strain control regions in optical devices

ABSTRACT

An optical device has a gallium and nitrogen containing substrate including a surface region and a strain control region, the strain control region being configured to maintain a quantum well region within a predetermined strain state. The device also has a plurality of quantum well regions overlying the strain control region.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.16/859,070, filed Apr. 27, 2020, which is a continuation of U.S.application Ser. No. 16/356,257, filed Mar. 18, 2019, which is adivisional of U.S. application Ser. No. 15/424,516, filed Feb. 3, 2017,which is a continuation of U.S. application Ser. No. 15/177,956, filedJun. 9, 2016, which is a divisional of U.S. application Ser. No.14/444,687, filed Jul. 28, 2014, which is a continuation of U.S.application Ser. No. 13/288,268, filed Nov. 3, 2011, which claimspriority to U.S. Provisional Application No. 61/410,794, filed Nov. 5,2010, each of which are incorporated herein by reference in theirentirety for all purposes.

BACKGROUND OF THE INVENTION

The invention is directed to optical devices and related methods. Inparticular, the invention provides a method and device for emittingelectromagnetic radiation using nonpolar or semipolar gallium containingsubstrates such as GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others.The invention provides a method and device using a gallium and nitrogencontaining substrate configured on the {20-21} family of planes or anoff-cut of the {20-21} family of planes towards the plus or minusc-plane and/or towards the a-plane according to one or more embodiments,but there can be other configurations. Still more particularly, theinvention provides a method and resulting structures that use highindium content InGaN or thick InGaN regions to facilitate manipulationof optical modes for desired optical properties in devices such as laserdiodes. Such high indium content InGaN or thick InGaN regions areintegrally coupled to a strain control region, which allows for suchintegration in an efficient and reliable manner. The invention can beapplied to optical devices, lasers, light emitting diodes, solar cells,photoelectrochemical water splitting and hydrogen generation,photodetectors, integrated circuits, and transistors, among otherdevices.

In 1960, the laser was first demonstrated by Theodore H. Maiman atHughes Research Laboratories in Malibu. This laser utilized asolid-state flash lamp-pumped synthetic ruby crystal to produce redlaser light at 694 nm. By 1964, blue and green laser output wasdemonstrated by William Bridges at Hughes Aircraft utilizing a gas laserdesign called an Argon ion laser. The Ar-ion laser utilized a noble gasas the active medium and produce laser light output in the UV, blue, andgreen wavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ionlaser had the benefit of producing highly directional and focusablelight with a narrow spectral output, but the wall plug efficiency was<0.1%, and the size, weight, and cost of the lasers were undesirable aswell.

As laser technology evolved, more efficient lamp pumped solid statelaser designs were developed for the red and infrared wavelengths, butthese technologies remained a challenge for blue and green and bluelasers. As a result, lamp pumped solid state lasers were developed inthe infrared, and the output wavelength was converted to the visibleusing specialty crystals with nonlinear optical properties. A green lamppumped solid state laser had 3 stages: electricity powers lamp, lampexcites gain crystal which lases at 1064 nm, 1064 nm goes into frequencyconversion crystal which converts to visible 532 nm. The resulting greenand blue lasers were called “lamped pumped solid state lasers withsecond harmonic generation” (LPSS with SHG) had wall plug efficiency of˜1%, and were more efficient than Ar-ion gas lasers, but were still tooinefficient, large, expensive, fragile for broad deployment outside ofspecialty scientific and medical applications. Additionally, the gaincrystal used in the solid state lasers typically had energy storageproperties which made the lasers difficult to modulate at high speedswhich limited its broader deployment.

To improve the efficiency of these visible lasers, high power diode (orsemiconductor) lasers were utilized. These “diode pumped solid statelasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nmdiode laser, 808 nm excites gain crystal, which lases at 1064 nm, 1064nm goes into frequency conversion crystal which converts to visible 532nm. The DPSS laser technology extended the life and improved the wallplug efficiency of the LPSS lasers to 5-10%, and furthercommercialization ensue into more high-end specialty industrial,medical, and scientific applications. However, the change to diodepumping increased the system cost and required precise temperaturecontrols, leaving the laser with substantial size, power consumptionwhile not addressing the energy storage properties which made the lasersdifficult to modulate at high speeds.

As high power laser diodes evolved and new specialty SHG crystals weredeveloped, it became possible to directly convert the output of theinfrared diode laser to produce blue and green laser light output. These“directly doubled diode lasers” or SHG diode lasers had 2 stages:electricity powers 1064 nm semiconductor laser, 1064 nm goes intofrequency conversion crystal which converts to visible 532 nm greenlight. These lasers designs are meant to improve the efficiency, costand size compared to DPSS-SHG lasers, but the specialty diodes andcrystals required make this challenging today. Additionally, while thediode-SHG lasers have the benefit of being directly modulate-able, theysuffer from severe sensitivity to temperature which limits theirapplication.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method and device for emitting electromagneticradiation using nonpolar or semipolar gallium containing substrates suchas GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others. Moreparticularly, the invention provides a method and device using a galliumand nitrogen containing {20-21} substrate or off cut of the {20-21}plane towards the plus or minus c-plane and/or towards the a-planeaccording to one or more embodiments, but there can be otherconfigurations such as a device using a gallium and nitrogen containing{30-31} substrate or off cut of the {30-31} plane, or the {10-11} or{11-22} family of planes. As used herein, the term “off-cut” or mis-cut”may be used interchangeably. Still more particularly, the inventionprovides a method and resulting structures that use high indium contentInGaN or thick InGaN regions to facilitate manipulation of optical modesfor desired optical properties in devices such as laser diodes. Suchhigh indium content InGaN or thick InGaN regions are integrally coupledto a strain control region, which allows for such integration in anefficient and reliable manner.

In general, laser devices made using gallium and nitrogen containingmaterials include a gallium and nitrogen containing substrate, activeregion, and electrode regions. In a preferred embodiment, an inclusionof a strain control region enables the incorporation of high indiumcontent and/or thick layers of InGaN or other layers such as low Alcontent InAlGaN layers within the epitaxial structure withoutdegradation of device characteristics, including photoluminescence,electroluminescence, and/or microfluorescence of the multi-quantum wellregions. Without inclusion of the strain control region, the cumulativestrain becomes too great such that the epitaxial structure becomesheavily defected with dislocations and other lattice imperfections.These defects degrade the material characteristics for use in opticaldevices, and they may exist at the interface between the high indiumcontent and/or thick InGaN layer(s) and the underlying layer, and/or inthe multi-quantum well active region, and/or in other regions.

Device characteristics for a laser device include a high indium contentand/or thick indium containing layer, such as InGaN, and strain controlregion are substantially similar to or better than the characteristicsof the laser diode without the high indium content and/or very thicklayers of InGaN. Without the strain control region, the interfacebetween the high indium content and/or thick layers of InGaN and theunderlying layer becomes heavily defected and the multi-quantum wellregions are significantly degraded with defects. Further, as shown inthe growth data and TEM images below, if the high indium content and/orthick InGaN layer exceeds some threshold value of strain, themulti-quantum well regions are plagued with defects.

The invention provides a strain control region, which facilitatesintegration of a high indium content region and/or thick InGaN regionthat leads to improved laser diode characteristics. Such characteristicsinclude confinement characteristics of optical modes, photoluminescence,electroluminescence, and others, alone or in combination. In suchembodiments, the strain control region enables integration of such highindium content region and/or thick InGaN region without introduction ofsubstantial defects to the multi-quantum well region or the regionbetween the high indium content region and/or thick InGaN region and/orthe multi-quantum well regions.

As further background, it is believed that high indium content and/orthick InGaN regions facilitate change and/or manipulation of an opticalfield and/or modes. As an example, the quantum well regions often have ahigher index of refraction than the lower index of refraction claddingregions formed from materials such as GaN. In general, as governed bysolutions to the Helmholtz (wave) equation, the optical field or mode ina laser waveguide structure becomes confined or pulled into regions ofhigher index such as the quantum well regions. By way of additionalindium content to the InGaN regions, the index of the InGaN regions isincreased. Such high indium content and/or thick InGaN regions canfacilitate confinement of the optical mode within the vicinity of thequantum well region and can cause the optical mode to be pulled away (ordownward) from the overlying p-type cladding regions. Confining theoptical mode within the vicinity of the quantum well region for highertotal confinement in the quantum wells and reducing the confinement inp-type layers leads to desirable laser device characteristics.

The invention provides a laser diode with a gallium and nitrogencontaining substrate having a surface region and a high indium contentor thick layer of InGaN or low Al content InAlGaN region overlying thesurface region. The device has a strain control region, which isconfigured to maintain at least a quantum well region within apredetermined strain and/or defect state. Optionally, the device has anoptical confinement region comprised of InGaN overlying the straincontrol region and a plurality of quantum well regions overlying theoptical confinement region. In other embodiments, the device includes anadditional optical confinement layer comprised of InGaN, or low Alcontent InAlGaN, overlying and above the quantum well region. In thepreferred embodiment, however, the high indium content and/or thicklayer of InGaN acts as an SCH region without the conventional SCH regionand acts as a “Super SCH” region(s) or layer(s), which facilitateoptical confinement of optical mode(s), and provides other features. Inother embodiments, the Super SCH may be combined with other SCH regions,among other features.

In a preferred embodiment, the gallium and nitrogen containing substratehas a surface region oriented in a semi-polar or non-polarconfiguration. As an example, the surface region is configured in a{20-21} orientation. In alternative embodiments, the surface region maybe configured in {30-31}, {10-11}, or {11-22} orientations. Dependingupon the embodiment, the surface region is configured to be in anoff-set of a {20-21} orientation.

The device also has a plurality of quantum well regions overlying thestrain control region. In a more preferred embodiment, the predeterminedstrain state also includes an interface region from high indium contentand/or thick InGaN region to the underlying growth structure regions orsubstrates, among others.

The invention provides a method for fabricating an optical device withina strain budget. The method includes providing a gallium and nitrogencontaining substrate having a surface region. The method includesdetermining an upper strain budget by cumulating strain information fromat least a plurality of quantum well regions, optical confinementlayers, and the high indium content and/or thick InGaN layers andintegrating the plurality of quantum well regions, optical confinementlayers, and the high indium content and/or thick InGaN layers with astrain control region to cause the upper strain budget to be within apredetermined strain budget. Preferably, the predetermined strain budgetis less than the upper strain budget.

The device also has a strain budget of Q characterizing a cumulativestrain characteristic associated with at least the plurality of quantumwell regions and the strained region or more preferably an entire growthstructure including the quantum well regions. The cumulative straincharacteristic excludes a contribution from the strain control region.The strain budget Q is greater than the predetermined strain state. Inan example, once the stain budget is exceeded, the epitaxial structureis subjected to an undesirable level of defects, which may be present atan interface region between the high indium content and/or thick InGaNlayer and the underlying layer, or in the MQW region, or other regions.In other embodiments, the defects may be distributed, localized,patterned, or random throughout one or more of the growth regions, suchas a gallium and nitrogen containing growth region.

Preferably, the defect threshold is above the upper level of defectswithin the plurality of quantum well regions without the strainadjustment region. In a preferred embodiment, the strained region is ahigh indium content and/or thick InGaN region, also called the Super SCHregion and may be used for optical confinement. The present strainadjustment region has a suitable thickness, indium content, and issometimes referred to as a strain control region.

Preferably, the defect state is fewer than a threshold number of defectscapable of causing a photoluminescence characteristic and aelectroluminescence characteristic to be below respective thresholdlevels. The device also has an optional optical confinement regionoverlying the strain control region and a plurality of quantum wellregions overlying the optical confinement region. In a preferredembodiment, the strained region is a high indium content and/or thickInGaN region, also called the Super SCH region and may be used foroptical confinement.

In an alternative embodiment, the invention provides an optical devicecomprising a gallium and nitrogen containing substrate and an overlyingstrain compensation region configured with a higher band gap material,which has a band gap higher than a lower band gap material within avicinity of the higher band gap material. As an example, the lower bandgap material includes both the high indium and/or thick InGaN regionsand the quantum well regions. In a specific embodiment, the higherbandgap material is comprised of GaN, AlGaN, or InAlGaN.

In a preferred embodiment, the gallium and nitrogen containing materialcan be a high indium content and/or thick InGaN containing material,which manipulates optical confinement of optical mode(s) within aquantum well region, p-type layer regions, and/or other regions withinthe epitaxial structure.

Moreover, the invention provides a method for designing an optical laserdiode device with desired confinement characteristics of the opticalmode, the method comprising selecting a strain control region configuredwith a dopant level, a thickness, and a position relative to amulti-quantum well region; and integrating the strain control regionwith a high indium content and/or thick InGaN material to provide adesired confinement of the optical mode within the p-type claddingregion and within the multi-quantum well region. In a preferredembodiment, the strain control region integrated with the high indiumcontent material or thick InGaN material facilitates fewer defects or adesired level of defects within a structure of the laser diode device,while eliminating such strain control region leads to a higher densityof defects and reduced performance levels in the optical device.

Still further, the invention provides an optical device, e.g., laserdiode. The device includes a gallium and nitrogen containing substratecomprising a surface region. The substrate is characterized by a firstlattice constant and a strained region overlying the surface region. Thestrain region is characterized by a second lattice constant. Preferably,the device has a strain control region formed overlying the strainedregion. Preferably, the strain control region characterized by a thirdlattice constant, which is substantially equivalent to the secondlattice constant. In a specific embodiment, the strain control region isconfigured to maintain a quantum well region within a predeterminedstrain state and/or to maintain a cumulative strain within an entiretyof a growth structure of the optical device within a predeterminedand/or desirable strain state, which has fewer defects for improvedoptical performance. Optionally, the device includes an additionaloptical confinement region overlying the strain control region and aplurality of quantum well regions overlying the optical confinementregion. In a preferred embodiment, the strained region comprises a highindium and/or thick InGaN material or materials, which also act as anoptical confinement region.

The device also has a gallium and nitrogen containing materialcomprising InGaN overlying the surface region. The device has a straincontrol region, the strain control region being configured to maintain acumulative strain within an entirety of a growth region including aquantum well region within a predetermined strain state. The device alsohas a plurality of quantum well regions overlying the strain controlregion. In a preferred embodiment, the plurality of quantum well regionsare configured to emit electromagnetic radiation characterized by anoptical mode spatially disposed at least partially within the quantumwell region. In a preferred embodiment, the gallium and nitrogencontaining material is configured with a thickness and an indium contentto manipulate a confinement of the optical mode and configured to absorba stray and/or leakage of the emission of electromagnetic radiation.

The gallium and nitrogen containing material can be configured to absorba stray and/or leakage of the emission of electromagnetic radiationwithout any ability to manipulate confined optical mode as governed bythe wave equation. In such embodiment, the material will be spatiallydisposed away from the optical mode and is configured for absorption ofthe stay or undesirable emissions, and the like. In a preferredembodiment, the material has a thickness of 5 nm to about 50 nm and anindium content of 14% to 25%, or alternatively, a thickness of 50 nm to200 nm with indium content of 5% to 15%, as well as other variations. Ina preferred embodiment, the gallium and nitrogen containing materialconfigured as the absorber is at least 0.5 microns below themulti-quantum well or other ranges such as 0.5 to 1.5 microns below, or1.5 to 3 microns below, or 3 to 10 microns below the multi-quantum well,or a spatial distance sufficient to absorb stray or leakage radiationwithout influencing the optical mode in the multi-quantum well. In otherembodiments, the absorbing material can be integrated, buried, ordisposed within a vicinity of the n-type cladding region.

Still further, the invention provides an optical device, e.g., laserdiode. The device includes a gallium and nitrogen containing substratecomprising a surface region, which may be oriented in either a semipolaror non-polar configuration. The device also has a first gallium andnitrogen containing material comprising InGaN overlying the surfaceregion and a first strain control region overlying the first gallium andnitrogen containing material. The device has a second gallium andnitrogen containing material comprising InGaN overlying the surfaceregion and a second strain control region overlying the first galliumand nitrogen containing material. In a specific embodiment, the devicehas a plurality of quantum well regions overlying the strain controlregion. In a preferred embodiment, the first strain control region ischaracterized by a higher band gap material than both the first galliumand nitrogen containing material and the quantum well regions and thesecond strain control region is characterized by a higher band gapmaterial than both the second gallium and nitrogen containing materialand the quantum well regions. Optionally, multiple intermediary straincontrol regions integrally coupled to a plurality of high indium and/orthick InGaN are included, as further described in the followingspecification.

Moreover, the invention includes an optical device. The device includesa gallium and nitrogen containing substrate comprising a surface regionand a first lattice constant and a strained region overlying the surfaceregion. Preferably, the strained region has a second lattice constant,which is larger than the first lattice constant. The device also has astrain control region having a third lattice constant, which issubstantially equivalent to the second lattice constant. The straincontrol region is configured to maintain at least a quantum well regionwithin a predetermined strain state. The device has an opticalconfinement region overlying the strain control region and a pluralityof quantum well regions overlying the optical confinement region. Eachof the plurality of quantum well regions has a fourth lattice constant,which is substantially equivalent to the second lattice constant.Preferably, the strain control region has a higher bandgap than thestrained region and the quantum well layers. In a preferred embodiment,each of the lattice constants is parallel to a projection of ac-direction. Additionally, the gallium and nitrogen containing substrateis configured on a semi-polar plane, such as (20-21) according to aspecific embodiment.

As used herein in examples, the terms “high indium content and/or thickInGaN layer(s) or regions” generally refers to an InGaN or like materialcapable of manipulating an optical mode or modes within a design of alaser diode. As an example, such InGaN region or layers arecharacterized by a thickness range and an indium concentration rangethat leads to excessive cumulative strain within the growth structuresand hence certain material degradation such as defects in the growthstructures without the present strain control region(s) or layer(s).That is, if there were no strain control region, such InGaN layers wouldbe detrimentally strained and lead to poor or undesirable materialcharacteristics such as photoluminescence, electroluminescence, andoptical device efficiency due certain defect characteristic in thestructure that would be present at the interface between the high indiumcontent and/or thick InGaN region and the underlying layer, and/or inthe multi-quantum well region, and/or in other regions. It should benoted that the InGaN layer(s) in its final form may be partially relaxeddue to the presence of defects and/or the strain control region,although it would be strained without such defects and/or stain controlregion. As an example, such cumulative strain often is a function of acombination of indium concentration and total thickness. For lowerindium content layers, much thicker layers are grown before cumulativestrain degradation occurs, while higher indium content may result inthinner layers before cumulative strain degradation occurs. Also, ahigher number of quantum wells may lead to higher cumulative stain thanfewer quantum wells.

In a specific embodiment, the present InGaN region can be configuredwith a suitable thickness and indium content for a laser diode device.Such InGaN region includes a thickness range from about 30 to about 80nm and about 11 to about 16% indium content. Alternatively, the InGaNregion includes a thickness range from about 70 to about 150 nm andabout 8 to about 13% indium content. Alternatively, the InGaN regionincludes a thickness ranging from about 140 to about 300 nm and about 5to about 9% indium content. Alternatively, the InGaN region includes athickness ranging from about 250 to about 500 nm and about 3 to about 6%indium content. Alternatively, the InGaN region includes a thicknessranging from about 10 nm to about 30 nm and about 15 to about 22% indiumcontent. Other variations can also exist depending upon the specificembodiment.

As used herein as an example, an SCH or optical confinement regionsincludes an InGaN or other indium containing layer(s) that yieldacceptable defect levels and material quality when incorporated in adevice structure containing a multiple quantum well active region onnon-polar or semi-polar Ga containing substrates such as {20-21}.Examples of SCH regions are InGaN layers with a thickness range fromabout 30 to about 80 nm and about 5 to about 8% indium content, or athickness range from about 70 to about 150 nm and about 3 to about 6%indium content, or a thickness ranging from about 140 to about 300 nmand about 2 to about 4% indium content, or a thickness ranging fromabout 250 to about 500 nm and about 1 to about 3% indium content.

As used herein the term Super SCH includes an InGaN or other indiumcontaining layer(s) that yield heavily defected material and hence poordevice properties due to excessive strain when incorporated in a devicestructure and not combined with strain control region(s) on nonpolar orsemipolar Ga containing substrates such as {20-21}. Once the Super SCHhas been integrated with the strain control region(s) acceptable,desirable, and even improved device performance occurs, as will bedescribed throughout the present specification and more particularlybelow. Examples of such Super SCH regions are InGaN layers with athickness range from about 30 to about 80 nm and about 11 to about 16%indium content, or a thickness range from about 70 to about 150 nm andabout 8 to about 13% indium content, or a thickness ranging from about140 to about 300 nm and about 5 to about 9% indium content, or athickness ranging from about 250 to about 500 nm and about 3 to about 6%indium content, or a thickness ranging from about 10 nm to about 30 nmand about 15 to about 22% indium content.

Additional benefits are achieved over pre-existing techniques using theinvention. In particular, the invention enables a cost-effective opticaldevice for laser applications. In a specific embodiment, the presentoptical device can be manufactured in a relatively simple and costeffective manner. Depending upon the embodiment, the present apparatusand method can be manufactured using conventional materials and/ormethods according to one of ordinary skill in the art. The present laserdevice uses a semipolar gallium nitride material capable of achieve agreen laser device, among others. In one or more embodiments, the laserdevice is capable of emitting long wavelengths such as those rangingfrom about 480 nm to greater than about 540 nm, but can be others suchas 540 nm to 660 nm. In one or more alternative embodiments, the laserdevice is capable of emitting long wavelengths such as those rangingfrom about 430 nm to greater than about 480 nm, but can be others. In apreferred embodiment, the present method and structure can be used tocontrol or engineer strain within the wave guiding layers and quantumwell region of laser devices. The present method and structure uses asemi-polar oriented substrate and growth structures that are capable ofa change in lattice structure to be larger and incorporate additionalindium, which leads to improved optical and electrical performance.Depending upon the embodiment, one or more of these benefits may beachieved. Of course, there can be other variations, modifications, andalternatives.

A further understanding of the nature and advantages of the inventionmay be realized by reference to the latter portions of the specificationand attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a laser diode on a {20-21} gallium and nitrogencontaining substrate having cleaved facets;

FIG. 2A is a simplified cross-sectional view diagram of a laser diode;

FIG. 2B is a cross-sectional view diagram of a laser diode;

FIG. 3 is an example of the refractive index and optical mode profilefor a green laser diode without a strain control region;

FIG. 4 is an example of growth characteristics of the laser diode ofFIG. 3 ;

FIG. 5 is an illustration of microfluorescence defect density formultiple laser diode structures;

FIG. 6 is a flow diagram of a method of tuning an active region for adesired strain characteristic;

FIG. 7 is an illustration of a method of providing waveguidecharacteristics for laser diode devices according to embodiments of theinvention.

FIG. 8 is an illustration of photoluminescence peak intensity formultiple laser diode structures;

FIG. 9 is an illustration of electroluminescence power for multiplelaser diode structures;

FIG. 10 is an example of the refractive index and optical mode profilefor a green laser diode;

FIG. 11 is an example of growth characteristics for the laser diode ofFIG. 10 ;

FIG. 12 is a transmission electron microscope image for the laser diodeof FIG. 10 ;

FIG. 13 illustrates micro-fluorescence of laser devices without straincontrol regions;

FIG. 14 is an example of growth characteristics for a laser diode ofFIG. 13 ;

FIGS. 15A and 15B are transmission electron microscope images ofcross-sections of laser diodes without strain control regions;

FIG. 16 is an example of the refractive index and optical mode profilefor a green laser diode;

FIG. 17 is an example of growth characteristics for the laser diode ofFIG. 16 ;

FIG. 18 is a simplified example of an active region of a laser diode;

FIG. 19 is a simplified example of growth characteristics for the laserdiode of FIG. 18 ;

FIG. 20 is a simplified example of the refractive index and optical modeprofile for a green laser diode;

FIG. 21 is a simplified example of growth characteristics for the laserdiode of FIG. 18 ;

FIG. 22A is an example of the refractive index and optical mode profileof a high indium content InGaN region above and below the MQW of a greenlaser diode;

FIG. 22B is an example of the refractive index and optical mode profilefor a daisy chain of high indium content and strain control regionsconfigured to modify the lattice constant within an active region of agreen laser diode;

FIG. 22C is an example of the refractive index and optical mode profileof an intermediate strain control region within a high indium contentand/or thick InGaN regions of a green laser diode;

FIG. 22D is an example of the refractive index and optical mode profileof an intermediate strain control region within a high indium contentand/or thick InGaN regions of a green laser diode;

FIG. 23 is an example of the refractive index and optical mode profileof a green laser diode having a strain control region exceeding a strainbudget;

FIG. 24 is an example of growth characteristics for a laser diode ofFIG. 23 ;

FIG. 25 shows transmission electron microscope images of the laser diodeof FIG. 23 ; and

FIGS. 26 and 27 are illustrations of RSM plots.

DETAILED DESCRIPTION OF THE INVENTION

We have discovered a way to design and fabricate high intensity greenlaser diode devices in a specific embodiment. In a specific embodiment,the present method and structure includes a high indium content and/orthick InGaN layers in the present epitaxial structures grown on {20-21}and offcuts thereof in gallium and nitrogen containing substrates. In apreferred embodiment, the high indium content and/or thick InGaN layersinclude 200-300 nm InGaN layers with 6% indium, 100 nm InGaN layers with10% indium, 60 nm InGaN layers with 13-15% indium, or 30 nm InGaN layerswith 15-18% indium within the present green laser diode epitaxialstructure without detriment to photoluminescence properties,electroluminescence properties, or defect density of the light emittingmultiple quantum well active region. In a specific embodiment, thepresent green laser diode epitaxial structure includes an n-type GaNcladding region(s), an n-side separate confinement hetereostructure(SCH), a multiple quantum well active region (MQW), a p-side SCH or GaNguiding layer, and electron blocking layer, and a p-type GaN claddingregion. However, with the inclusion of the high indium content and/orthick InGaN layer, not all of these layers would be provided in apreferred epitaxial structure. For example, the n-side SCH layer can beremoved such that the high indium content and/or thick InGaN layer wouldbe used to modify the optical confinement properties of the mode andhence would act as an SCH region without the SCH region and therefore a“Super-SCH” region. In other embodiments, the combination of an SCH andhigh indium content and/or thick InGaN layers are included.

In a preferred embodiment, the method and structure includes use of acombination of the high indium content and/or thick InGaN layers with astrain control region. As an example in such embodiments, in order toinclude these high indium content and/or thick InGaN layers that act asthe “super-SCH”, one preferably includes the strain control region. Thatis, the strain control region exists spatially between the high indiumcontent and/or thick InGaN layers and the MQW. The strain control regionperforms some sort of strain compensation function and ultimatelysuppresses the defect density at the interface between the high indiumcontent and/or thick InGaN layer and the underlying layer(s), in themultiple quantum well region, or in other regions, as will be furtherexplained and described below. It also limits the defect density withinthe MQW in a specific embodiment. The strain control region is generallycomposed of a material with higher bandgap than both the high indiumcontent and/or thick InGaN layer and the quantum well layers. The straincontrol region is preferably 5 nm to 20 nm or 20 nm to 50 nm andcomprised of GaN, AlGaN, or InAlGaN and can be doped.

As an example, the present method and structures lead to improvedoptical device performance, as describe below. In a specific embodiment,the present method and structure includes a high indium content and/orthick InGaN region within an optical device.

As an example by including the high indium content and/or thick InGaNlayer in the waveguide design as the Super SCH, the optical mode can beasymmetrically shaped such that it is skewed away from the p-typeregions to reduce optical confinement in the p-type regions. Since thep-type regions are absorbing to the optical field, by skewing theoptical mode away from the p-type regions the modal loss in the lasercavity will be reduced. This will enable higher slope efficiency andreduced threshold current in a laser diode for an overall increased wallplug efficiency. As an example, embodiments are shown in at least FIGS.10 and 16 . Also as an example, the Super SCH and strain control regionsare spatially positioned below the present n-side SCH and MQW. In theseembodiments, the optical mode is pulled downward toward the n-typecladding. However, in this embodiment the optical confinement in the MQWis also reduced, which will reduce the gain of the laser diode.

By including high indium content InGaN layer(s) below or below and abovethe multiple quantum well active region in close vicinity, the opticalmode in the laser active region is preferably concentrated around and/orwithin the multiple quantum wells or slight variations in spatialregions within and around the multiple quantum wells. That is, theoptical mode is pulled inward toward the MQW and high-indium content andthus the field intensity will be stronger around the MQW. This willincrease the optical confinement in the MQW and hence increase the modalgain, which is desirable. Since the threshold current density isdictated by the modal gain and the losses, an increased gain will allowfor lower threshold current densities. Further, by pulling the modeinward toward the MQW and high indium content InGaN layer, the opticalconfinement in the p-type regions can be reduced for reduced modallosses. Example embodiments with high indium content Super SCH layersbelow the MQW are given in at least FIGS. 18 and 20 . An exampleembodiment of the Super SCH layers positioned above and below the MQW isgiven in at least FIG. 22 a.

By growing high indium content and/or thick InGaN layers that partiallyrelax by misfit dislocations at a lower interface region between thesubstrate and overlying growth regions, the native lattice constant ofthe epitaxial stack is modified as it becomes identical to InGaN withsome or a certain indium content. By coherently depositing the higherbandgap strain control region on top of the high indium content and/orthick InGaN layer, the strain control layer takes on the new nativelattice constant, which as stated, is closer to InGaN with some indiumconcentration. Since this strain control region limits the defects andenables the growth of high quality light emitting MQW regions, thisindicates that these high quality MQW regions are strained to adifferent lattice constant than the initial GaN lattice constant of thesubstrate. Since the new lattice constant is matched to InGaN with someconcentration of indium, the MQW active region will be less strained.Because strain is a main degradation mechanism as more indium is addedto the MQW to extend the emission wavelength, this is a desirablefeature for extending the MQW emission wavelength to the yellow and redregimes, and possibly even to improve the efficiency in the greenregime. By modifying the lattice constant to InGaN with some indiumcontent with the partially relaxed high indium content and/or thickInGaN layers and then growing a strain control region to limit defectsand maintain high quality MQW quality, increased emission efficiency canbe achieved in the red, yellow, and green wavelength regimes onsemipolar GaN.

In a specific embodiment, the invention provides an optical device,e.g., laser, LED. The device includes a gallium and nitrogen containingsubstrate (e.g., GaN) comprising a surface region oriented in either asemipolar or non-polar configuration, but can be others. The device alsohas a gallium and nitrogen containing material comprising InGaNoverlying the surface region. The device has a strain control region,the strain control region being configured to maintain a cumulativestrain within an entirety of a growth region including a quantum wellregion within a predetermined strain state. The device also has aplurality of quantum well regions overlying the strain control region.In a preferred embodiment, the plurality of quantum well regions areconfigured to emit electromagnetic radiation characterized by an opticalmode spatially disposed at least partially within the quantum wellregion. In a preferred embodiment, the gallium and nitrogen containingmaterial is configured with a thickness and an indium content tomanipulate a confinement of the optical mode and configured to absorb astray and/or leakage of the emission of electromagnetic radiation. In analternative specific embodiment, the gallium and nitrogen containingmaterial can be configured to absorb a stray and/or leakage of theemission of electromagnetic radiation without any ability to manipulateoptical mode. In such embodiment, the material will be spatiallydisposed away from the optical mode and is configured for absorption ofthe stay or undesirable emissions, and the like. In a preferredembodiment, the material has a thickness of 5 nm to about 50 nm and anindium content of 14% to 25%, or alternatively, a thickness of 50 nm to200 nm with indium content of 5% to 15%, as well as other variations. Ina preferred embodiment, the gallium and nitrogen containing materialconfigured as the absorber is at least 0.5 microns below themulti-quantum well or other ranges such as 0.5 to 1.5 microns below, or1.5 to 3 microns below, or 3 to 10 microns below the multi-quantum well,or a spatial distance sufficient to absorb stray or leakage radiationwithout influencing the optical mode in the multi-quantum well. In otherembodiments, the absorbing material can be integrated, buried, ordisposed within a vicinity of the n-type cladding region.

In a specific embodiment, the present laser device can be employed ineither a semipolar or non-polar gallium containing substrate, asdescribed below. As used herein, the term “substrate” can mean the bulksubstrate or can include overlying growth structures such as a galliumand nitrogen containing epitaxial region, or functional regions such asn-type GaN, combinations, and the like. We have also explored epitaxialgrowth and cleave properties on semipolar crystal planes orientedbetween the nonpolar m-plane and the polar c-plane. In particular, wehave grown on the {30-31} and {20-21} families of crystal planes. Wehave achieved promising epitaxy structures and cleaves that will createa path to efficient laser diodes operating at wavelengths from about 400nm to green, e.g., 500 nm to 540 nm. These results include bright blueepitaxy in the 450 nm range, bright green epitaxy in the 520 nm range,and smooth cleave planes orthogonal to the projection of thec-direction. It is desirable to align the laser cavities parallel to theprojection of the c-direction for maximum gain on this family of crystalplanes.

Although it was believed that a higher gain would be offered in theprojection of the c-direction than would be available in thea-direction, it is also desirable to form a high quality cleavage planeorthogonal to a stripe oriented in the projection of the c-direction.More specifically, we desired a high quality cleavage plane orthogonalto the [10-1-7] for a laser stripe formed on the {20-21} plane. In oneor more preferred embodiments, we determined a high quality cleave planesubstantially orthogonal to the projection of the c-direction, [10-1-7].In particular, we determined that if a top side skip-scribe scribingtechnique is used followed by a break step a high quality smooth andvertical cleaved facet would be formed on the upper portion of thecleave face according to one or more embodiments. Below the upperportion of the cleave face the facet becomes angled, which may not beoptimum for a laser diode mirror according to one or more embodiments.In other embodiments, however, such angled cleave characteristic isdesirable for laser fabrication since the laser mirror will bepositioned on top of the substrate where the cleave face is vertical. Inone or more embodiments, when the sample is back side laser scribed andthen broken, an angled, but smooth cleave face is formed. Such a smoothcleave face may be desirable for lasers, but it is not the mostpreferable since the laser mirror will be tilted. The top-side skipscribe technique looks more preferably according to one or moreembodiments.

FIG. 1 is a perspective view of a laser device 100 fabricated on anoff-cut m-plane {20-21} substrate according to an embodiment of theinvention. As shown, the optical device includes a gallium nitridesubstrate member 101 having the off-cut m-plane crystalline surfaceregion. In a specific embodiment, the gallium nitride substrate memberis a bulk GaN substrate characterized by having a semipolar or non-polarcrystalline surface region, but can be others. In a specific embodiment,the bulk nitride GaN substrate comprises nitrogen and has a surfacedislocation density between about 10E5 cm-2 and about 10E7 cm-2 or below10E5 cm-2. The nitride crystal or wafer may comprise AlxInyGal-x-yN,where 0≤x, y, x+y≤1. In one specific embodiment, the nitride crystalcomprises GaN. In one or more embodiments, the GaN substrate hasthreading dislocations, at a concentration between about 10E5 cm-2 andabout 10E8 cm-2, in a direction that is substantially orthogonal oroblique with respect to the surface. As a consequence of the orthogonalor oblique orientation of the dislocations, the surface dislocationdensity is between about 10E5 cm-2 and about 10E7 cm-2 or below about10E5 cm-2. In a specific embodiment, the device can be fabricated on aslightly off-cut semipolar substrate as described in U.S. Ser. No.12/749,466 filed Mar. 29, 2010, which claims priority to U.S.Provisional No. 61/164,409 filed Mar. 28, 2009, commonly assigned, andhereby incorporated by reference herein.

In a specific embodiment on the {20-21} GaN, the device has a laserstripe region formed overlying a portion of the off-cut crystallineorientation surface region. In a specific embodiment, the laser striperegion is characterized by a cavity orientation substantially in aprojection of a c-direction, which is substantially normal to ana-direction. In a specific embodiment, the laser strip region has afirst end 107 and a second end 109. In a preferred embodiment, thedevice is formed on a projection of a c-direction on a {20-21} galliumand nitrogen containing substrate having a pair of cleaved mirrorstructures, which face each other. In a preferred embodiment, the firstcleaved facet comprises a reflective coating and the second cleavedfacet comprises no coating, an antireflective coating, or exposesgallium and nitrogen containing material.

In a preferred embodiment, the device has a first cleaved facet providedon the first end of the laser stripe region and a second cleaved facetprovided on the second end of the laser stripe region. In one or moreembodiments, the first cleaved facet is substantially parallel with thesecond cleaved facet. Mirror surfaces are formed on each of the cleavedsurfaces. The first cleaved facet comprises a first mirror surface. In apreferred embodiment, the first mirror surface is provided by a top-sideskip-scribe scribing and breaking process. The scribing process can useany suitable techniques, such as a diamond scribe or laser scribe orcombinations. In a specific embodiment, the first mirror surfacecomprises a reflective coating. The reflective coating is selected fromsilicon dioxide, hafnia, and titania, tantalum pentoxide, zirconia,including combinations, and the like. Depending upon the embodiment, thefirst mirror surface can also comprise an anti-reflective coating.

Also in a preferred embodiment, the second cleaved facet comprises asecond mirror surface. The second mirror surface is provided by a topside skip-scribe scribing and breaking process according to a specificembodiment. Preferably, the scribing is diamond scribed or laser scribedor the like. In a specific embodiment, the second mirror surfacecomprises a reflective coating, such as silicon dioxide, hafnia, andtitania, tantalum pentoxide, zirconia, combinations, and the like. In aspecific embodiment, the second mirror surface comprises ananti-reflective coating.

In a specific embodiment, the laser stripe has a length and width. Thelength ranges from about 50 microns to about 3000 microns, but ispreferably between 400 microns and 1000 microns. The stripe also has awidth ranging from about 0.5 microns to about 50 microns, but ispreferably between 0.8 microns and 3 microns, but can be otherdimensions. In a specific embodiment, the present device has a widthranging from about 0.5 microns to about 1.5 microns, a width rangingfrom about 1.5 microns to about 3.0 microns, and others. In a specificembodiment, the width is substantially constant in dimension, althoughthere may be slight variations. The width and length are often formedusing a masking and etching process, which are commonly used in the art.

In a specific embodiment, the invention provides an alternative devicestructure capable of emitting 501 nm and greater (e.g., 525 nm) light ina ridge laser embodiment. The device is provided with one or more of thefollowing epitaxially grown elements, but is not limiting, and inreference to FIG. 2A.

-   -   an n-GaN cladding region with a thickness of 50 nm to about 6000        nm with a Si or oxygen doping level of about 5E16 cm-3 to 1E19        cm-3    -   an InGaN region of a high indium content and/or thick InGaN        layer(s) or Super SCH region;    -   a higher bandgap strain control region overlying the InGaN        region;    -   optionally, an SCH region overlying the InGaN region;    -   multiple quantum well active region layers comprised of three to        five or four to six 3.0-5.5.0 nm InGaN quantum wells separated        by 1.5-10.0 nm GaN barriers    -   optionally, a p-side SCH layer comprised of InGaN with molar a        fraction of indium of between 1% and 10% and a thickness from 15        nm to 100 nm    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 10        nm to 15 nm and doped with Mg.    -   a p-GaN cladding layer with a thickness from 400 nm to 1000 nm        with Mg doping level of 5E17 cm-3 to 1E19 cm-3    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 1E20 cm-3 to 1E21 cm-3

In a specific embodiment, the laser device is fabricated on a {20-21}substrate.

FIG. 2A is a cross-sectional view of a laser device 200 fabricated on a{20-21} substrate according to an embodiment of the invention. As shown,the laser device includes gallium nitride substrate 203, which has anunderlying n-type metal back contact region 201. An n-type claddingregion is formed overlying the gallium nitride substrate. Overlying thegallium nitride substrate and n-type cladding region is a high indiumcontent and/or thick InGaN layer 202. In a specific embodiment, thedevice has a strain control layer 204 overlying the high indium contentand/or thick InGaN layer. In a specific embodiment, the metal backcontact region is made of a suitable material such as those noted belowand others.

In a specific embodiment, the device also has an overlying n-typegallium nitride layer 205, an n-type cladding layer, a high indiumcontent and/or thick InGaN layer 202, a strain control layer 204, anactive region 207, and an overlying p-type gallium nitride layerstructured as a laser stripe region 209. In a specific embodiment, eachof these regions is formed using at least an epitaxial depositiontechnique of metal organic chemical vapor deposition (MOCVD), molecularbeam epitaxy (MBE), or other epitaxial growth techniques suitable forGaN growth. In a specific embodiment, the epitaxial layer is a highquality epitaxial layer overlying the n-type gallium nitride layer. Insome embodiments the high quality layer is doped, for example, with Sior O to form n-type material, with a dopant concentration between about1E16 cm-3 and 1E20 cm-3.

In a specific embodiment, an n-type AluInvGal-u-vN layer, where 0≤u, v,u+v≤1, is deposited on the substrate. In a specific embodiment, thecarrier concentration may lie in the range between about 1E16 cm-3 and1E20 cm-3. The deposition may be performed using metalorganic chemicalvapor deposition (MOCVD) or molecular beam epitaxy (MBE).

As an example, the bulk GaN substrate is placed on a susceptor in anMOCVD reactor. After closing, evacuating, and back-filling the reactor(or using a load lock configuration) to atmospheric pressure, thesusceptor is heated to a temperature between about 1000 and about 1200degrees Celsius in the presence of a nitrogen-containing gas. In onespecific embodiment, the susceptor is heated to approximately 900 to1100 degrees Celsius under flowing ammonia. A flow of agallium-containing metalorganic precursor, such as trimethylgallium(TMG) or triethylgallium (TEG) is initiated, in a carrier gas, at atotal rate between approximately 1 and 50 standard cubic centimeters perminute (sccm). The carrier gas may comprise hydrogen, helium, nitrogen,or argon. The ratio of the flow rate of the group V precursor (ammonia)to that of the group III precursor (trimethylgallium, triethylgallium,trimethylindium, trimethylaluminum) during growth is between about 2000and about 15000. A flow of disilane in a carrier gas, with a total flowrate of between about 0.1 and 10 sccm, is initiated.

In a specific embodiment, the high indium content and/or thick InGaNlayer(s) or regions comprises an InGaN or like material capable ofmanipulating an optical mode or modes within a design of a laser diode.As an example, such InGaN region or layers are characterized by athickness range and an indium concentration range that leads toexcessive cumulative strain within the growth structures and hencecertain material degradation in the growth structures without thepresent strain control region(s) or layer(s). That is, if there were nostrain control region, such InGaN layers would be detrimentally strainedand lead to poor or undesirable material characteristics such asphotoluminescence, electroluminescence, and optical device efficiencyresulting from certain defect characteristics in the structure thatcould be located in the multi-quantum well region, and/or at theinterface between the high indium content and/or thick InGaN region andthe underlying layer, and/orin other regions. As an example, suchcumulative strain often is a function of a combination of indiumconcentration and total thickness. For lower indium content layers, muchthicker layers are grown before cumulative strain degradation occurs,while higher indium content may result in thinner layers beforecumulative strain degradation occurs. Also, a higher number of quantumwells may lead to higher cumulative stain than fewer quantum wells.

In a specific embodiment, the present InGaN region can be configuredwith a suitable thickness and indium content for a laser diode device.Such InGaN region includes a thickness range from about 30 to about 80nm and about 11 to about 16% indium content. Alternatively, the InGaNregion includes a thickness range from about 70 to about 150 nm andabout 8 to about 12% indium content. Alternatively, the InGaN regionincludes a thickness ranging from about 140 to about 300 nm and about 5to about 9% indium content. Alternatively, the InGaN region includes athickness ranging from about 250 to about 500 nm and about 3 to about 6%indium content. Alternatively, the InGaN region includes a thicknessranging from about 10 nm to about 30 nm and about 15 to about 22% indiumcontent.

In a specific embodiment, the strain control layer(s) or regions, whichalso serves as a compensation region, comprises a higher band gapmaterial, which has a band gap higher than a lower band gap materialwithin a vicinity of the higher band gap material. As an example, thelower band gap material includes both the high indium or thick InGaNregions and the quantum well regions. In a specific embodiment, thehigher bandgap material is comprised of GaN, AlGaN, or InAlGaN. In aspecific embodiment, the laser stripe region is made of the p-typegallium nitride layer 209. In a specific embodiment, the laser stripe isprovided by an etching process selected from dry etching or wet etching.In a preferred embodiment, the etching process is dry, but can beothers. As an example, the dry etching process is an inductively coupledprocess using chlorine bearing species or a reactive ion etching processusing similar chemistries. Again as an example, the chlorine bearingspecies are commonly derived from chlorine gas or the like. The devicealso has an overlying dielectric region, which exposes 213 contactregion. In a specific embodiment, the dielectric region is an oxide suchas silicon dioxide or silicon nitride, but can be others. The contactregion is coupled to an overlying metal layer 215. The overlying metallayer is a multilayered structure containing gold and platinum (Pt/Au)or nickel and gold (Ni/Au), but can be others.

In a specific embodiment, the laser device has active region 207. Theactive region can include one to twenty quantum well regions accordingto one or more embodiments. As an example following deposition of then-type AluInvGal-u-vN layer for a predetermined period of time, so as toachieve a predetermined thickness, an active layer is deposited. Theactive layer may comprise a single quantum well or a multiple quantumwell, with 2-10 quantum wells. The quantum wells may comprise InGaNwells and GaN barrier layers. In other embodiments, the well layers andbarrier layers comprise AlwInxGal-w-xN and AlyInzGal-y-zN, respectively,where 0≤w, x, y, z, w+x, y+z≤1, where w<u, y and/or x>v, z so that thebandgap of the well layer(s) is less than that of the barrier layer(s)and the n-type layer. The well layers and barrier layers may each have athickness between about 1 nm and about 15 nm. In another embodiment, theactive layer comprises a double heterostructure, with an InGaN orAlwInxGal-w-xN layer about 10 nm to 100 nm thick surrounded by GaN orAlyInzGal-y-zN layers, where w<u, y and/or x>v, z. The composition andstructure of the active layer are chosen to provide light emission at apreselected wavelength. The active layer may be left undoped (orunintentionally doped) or may be doped n-type or p-type.

In a specific embodiment, the active region can also include an electronblocking region, and a separate confinement heterostructure. In someembodiments, an electron blocking layer is preferably deposited. Theelectron-blocking layer may comprise AlsIntGal-s-tN, where 0≤s, t,s+t≤1, with a higher bandgap than the active layer, and may be dopedp-type. In one specific embodiment, the electron blocking layercomprises AlGaN. In another embodiment, the electron blocking layercomprises an AlGaN/GaN super-lattice structure, comprising alternatinglayers of AlGaN and GaN, each with a thickness between about 0.2 nm andabout 5 nm. In another embodiment the electron blocking layer comprisesInAlGaN. In yet another embodiment there is not electron blocking layer.

As noted, the p-type gallium nitride structure, is deposited above theelectron blocking layer and active layer(s). The p-type layer may bedoped with Mg, to a level between about 10E16 cm-3 and 10E22 cm-3, andmay have a thickness between about 5 nm and about 1000 nm. The outermost1-50 nm of the p-type layer may be doped more heavily than the rest ofthe layer, so as to enable an improved electrical contact. In a specificembodiment, the laser stripe is provided by an etching process selectedfrom dry etching or wet etching. In a preferred embodiment, the etchingprocess is dry, but can be others. The device also has an overlyingdielectric region, which exposes 213 contact region.

In a specific embodiment, the metal contact is made of suitablematerial. The reflective electrical contact may comprise at least one ofsilver, gold, aluminum, nickel, platinum, rhodium, palladium, chromium,or the like. The electrical contact may be deposited by thermalevaporation, electron beam evaporation, electroplating, sputtering, oranother suitable technique. In a preferred embodiment, the electricalcontact serves as a p-type electrode for the optical device. In anotherembodiment, the electrical contact serves as an n-type electrode for theoptical device.

In a specific embodiment, the invention provides an alternative devicestructure capable of emitting light in a ridge laser embodiment. Thedevice is provided with one or more of the following epitaxially grownelements, but is not limiting, and in reference to FIG. 2B.

-   -   an n-GaN cladding region with a thickness of 50 nm to about 6000        nm with a Si or oxygen doping level of about 5E16 cm-3 to 1E19        cm-3    -   an InGaN region of a high indium content and/or thick InGaN        layer(s) or Super SCH region;    -   a higher bandgap region overlying the InGaN region;    -   an InGaN region of a high indium content and/or thick InGaN        layer(s) or Super SCH region;    -   a higher bandgap region overlying the InGaN region;    -   optionally, an SCH region overlying the InGaN region;    -   a strain control region overlying the higher bandgap region;    -   multiple quantum well active region layers comprised of four to        six 3.0-5.5.0 nm InGaN quantum wells separated by 1.5-10.0 nm        GaN or InGaN barriers    -   optionally, a p-side SCH layer comprised of InGaN with molar a        fraction of indium of between 1% and 10% and a thickness from 15        nm to 100 nm    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 10        nm to 15 nm and doped with Mg.    -   a p-GaN cladding layer with a thickness from 300 nm to 1000 nm        with Mg doping level of 5E17 cm-3 to 3E19 cm-3    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 5E19 cm-3 to 1E21 cm-3

In a specific embodiment, the laser device is fabricated on a {20-21}substrate.

FIG. 2B is a cross-sectional view of a laser device 200 fabricated on a{20-21} substrate according to an embodiment of the invention. As shown,the laser device includes gallium nitride substrate 203, which has anunderlying n-type metal back contact region 201. An n-type claddinglayer is formed overlying the gallium nitride substrate. Overlying thegallium nitride substrate and the n-type cladding layer is a high indiumcontent and/or thick InGaN layer 202. In a specific embodiment, thedevice has a strain control layer 204 overlying the high indium contentand/or thick InGaN layer. As shown, multiple strain control layers canbe integrated with multiple high indium content and/or thick InGaNlayers. In a specific embodiment, the metal back contact region is madeof a suitable material such as those noted below.

In a specific embodiment, the device also has an overlying n-typegallium nitride layer 205, an n-type cladding layer, a high indiumcontent and/or thick InGaN layer 202, a stain control layer 204, anactive region 207, and an overlying p-type gallium nitride layerstructured as a laser stripe region 209. In a specific embodiment, eachof these regions is formed using at least an epitaxial depositiontechnique of metal organic chemical vapor deposition (MOCVD), molecularbeam epitaxy (MBE), or other epitaxial growth techniques suitable forGaN growth. In a specific embodiment, the epitaxial layer is a highquality epitaxial layer overlying the n-type gallium nitride layer. Insome embodiments the high quality layer is doped, for example, with Sior O to form n-type material, with a dopant concentration between about10E16 cm-3 and 10E20 cm-3.

An n-type AluInvGal-u-vN layer, where 0≤u, v, u+v≤1, is deposited on thesubstrate. In a specific embodiment, the carrier concentration may liein the range between about 10E16 cm-3 and 10E20 cm-3. The deposition maybe performed using metalorganic chemical vapor deposition (MOCVD) ormolecular beam epitaxy (MBE).

As an example, the bulk GaN substrate is placed on a susceptor in anMOCVD reactor. After closing, evacuating, and back-filling the reactor(or using a load lock configuration) to atmospheric pressure, thesusceptor is heated to a temperature between about 1000 and about 1200degrees Celsius in the presence of a nitrogen-containing gas. In onespecific embodiment, the susceptor is heated to approximately 900 to1100 degrees Celsius under flowing ammonia. A flow of agallium-containing metalorganic precursor, such as trimethylgallium(TMG) or triethylgallium (TEG) is initiated, in a carrier gas, at atotal rate between approximately 1 and 50 standard cubic centimeters perminute (sccm). The carrier gas may comprise hydrogen, helium, nitrogen,or argon. The ratio of the flow rate of the group V precursor (ammonia)to that of the group III precursor (trimethylgallium, triethylgallium,trimethylindium, trimethylaluminum) during growth is between about 2000and about 15000. A flow of disilane in a carrier gas, with a total flowrate of between about 0.1 and 10 sccm, is initiated.

The high indium content and/or thick InGaN layer(s) or regions comprisesan InGaN or like material capable of manipulating an optical mode ormodes within a design of a laser diode. As an example, such InGaN regionor layers are characterized by a thickness range and an indiumconcentration range that leads to excessive cumulative strain within thegrowth structures and hence certain material degradation in the growthstructures without the presence of strain control region(s) or layer(s).That is, if there were no strain control region, such InGaN layers wouldbe detrimentally strained and lead to poor or undesirable materialcharacteristics such as photoluminescence, electroluminescence, andoptical device efficiency due to certain defect characteristics withinthe structure that could be located in the quantum well region, and/orat the interface between the high indium content and/or thick InGaNlayer and the underlying layer, and/or in other regions. It should benoted that the InGaN layer(s) in its final form may be partially relaxeddue to the presence of defects and/or the strain control region,although it would be strained without such defects and/or stain controlregion. As an example, such cumulative strain often is a function of acombination of indium concentration and total thickness. For lowerindium content layers, much thicker layers are grown before cumulativestrain degradation occurs, while higher indium content may result inthinner layers before cumulative strain degradation occurs. Also, ahigher number of quantum wells may lead to higher cumulative stain thanfewer quantum wells.

The present InGaN region can be configured with a suitable thickness andindium content for a laser diode device. Such InGaN region includes athickness range from about 30 to about 80 nm and about 11 to about 16%indium content. Alternatively, the InGaN region includes a thicknessrange from about 70 to about 150 nm and about 8 to about 12% indiumcontent. Alternatively, the InGaN region includes a thickness rangingfrom about 140 to about 300 nm and about 5 to about 9% indium content.Alternatively, the InGaN region includes a thickness ranging from about250 to about 500 nm and about 3 to about 6% indium content.Alternatively, the InGaN region includes a thickness ranging from about10 to about 30 nm and about 16 to about 21% indium content.

The strain control layer(s) or regions, which also serves as acompensation region, comprises a higher band gap material, which has aband gap higher than a lower band gap material within a vicinity of thehigher band gap material. As an example, the lower band gap materialincludes both the high indium or thick InGaN regions and the quantumwell regions. In a specific embodiment, the higher bandgap material iscomprised of GaN, AlGaN, or InAlGaN. In a specific embodiment, the laserstripe region is made of the p-type gallium nitride layer 209. In aspecific embodiment, the laser stripe is provided by an etching processselected from dry etching or wet etching. In a preferred embodiment, theetching process is dry, but can be others. As an example, the dryetching process is an inductively coupled process using chlorine bearingspecies or a reactive ion etching process using similar chemistries.Again as an example, the chlorine bearing species are commonly derivedfrom chlorine gas or the like. The device also has an overlyingdielectric region, which exposes 213 contact region. In a specificembodiment, the dielectric region is an oxide such as silicon dioxide orsilicon nitride, but can be others. The contact region is coupled to anoverlying metal layer 215. The overlying metal layer is a multilayeredstructure containing gold and platinum (Pt/Au) or nickel and gold(Ni/Au).

The laser device has active region 207. The active region can includeone to twenty quantum well regions according to one or more embodiments.As an example following deposition of the n-type AluInvGal-u-vN layerfor a predetermined period of time, so as to achieve a predeterminedthickness, an active layer is deposited. The active layer may comprise asingle quantum well or a multiple quantum well, with 2-10 quantum wells.The quantum wells may comprise InGaN wells and GaN barrier layers. Inother embodiments, the well layers and barrier layers compriseAlwInxGal-w-xN and AlyInzGal-y-zN, respectively, where 0≤w, x, y, z,w+x, y+z≤1, where w<u, y and/or x>v, z so that the bandgap of the welllayer(s) is less than that of the barrier layer(s) and the n-type layer.The well layers and barrier layers may each have a thickness betweenabout 1 nm and about 15 nm. In another embodiment, the active layercomprises a double heterostructure, with an InGaN or AlwInxGal-w-xNlayer about 10 nm to 100 nm thick surrounded by GaN or AlyInzGal-y-zNlayers, where w<u, y and/or x>v, z. The composition and structure of theactive layer are chosen to provide light emission at a preselectedwavelength. The active layer may be left undoped (or unintentionallydoped) or may be doped n-type or p-type.

The active region can also include an electron blocking region, and aseparate confinement heterostructure. In some embodiments, an electronblocking layer is preferably deposited. The electron-blocking layer maycomprise AlsIntGal-s-tN, where 0≤s, t, s+t≤1, with a higher bandgap thanthe active layer, and may be doped p-type. In one specific embodiment,the electron blocking layer comprises AlGaN. In another embodiment, theelectron blocking layer comprises an AlGaN/GaN super-lattice structure,comprising alternating layers of AlGaN and GaN, each with a thicknessbetween about 0.2 nm and about 5 nm. In another embodiment the electronblocking layer comprises InAlGaN. In yet another embodiment there is notelectron blocking layer.

As noted, the p-type gallium nitride structure, is deposited above theelectron blocking layer and active layer(s). The p-type layer may bedoped with Mg, to a level between about 10E16 cm-3 and 10E22 cm-3, andmay have a thickness between about 5 nm and about 1000 nm. The outermost1-50 nm of the p-type layer may be doped more heavily than the rest ofthe layer, so as to enable an improved electrical contact. In a specificembodiment, the laser stripe is provided by an etching process selectedfrom dry etching or wet etching. In a preferred embodiment, the etchingprocess is dry. The device also has an overlying dielectric region,which exposes 213 contact region. In a specific embodiment, thedielectric region is an oxide such as silicon dioxide.

The metal contact is made of suitable material. The reflectiveelectrical contact may comprise at least one of silver, gold, aluminum,nickel, platinum, rhodium, palladium, chromium, or the like. Theelectrical contact may be deposited by thermal evaporation, electronbeam evaporation, electroplating, sputtering, or another suitabletechnique. In a preferred embodiment, the electrical contact serves as ap-type electrode for the optical device. In another embodiment, theelectrical contact serves as an n-type electrode for the optical device.

FIG. 3 is a simplified example of a simulation of the refractive indexand mode profile for a green laser diode structure without a high indiumcontent and/or thick InGaN (Super SCH) region or strain control regionaccording to an embodiment of the invention. As shown, a vertical axisillustrates a refractive index plotted against a waveguide position fora baseline laser diode device, which will be explained in more detailbelow. The device has a gallium and nitrogen containing substratecomprising a surface region in a specific embodiment. The substrate ispreferably GaN or other suitable material. In a specific embodiment, thesurface region includes an n-type cladding region such as GaN or others.As also shown, the device includes an n-type SCH region, which isoverlying the GaN. The n-type SCH region comprises InGaN. Overlying thecladding region are a plurality of quantum well regions having anInGaN/GaN alternating structure. The device also has an upper guide orSCH, which can be either GaN or InGaN. The device also has an electronblocking region, such as those made by AlGaN, AlInN, AlInGaN or othersuitable materials. In a specific embodiment, the device has anoverlying p-type cladding region, such as GaN, which is doped.

FIG. 4 is an example of growth characteristics of the laser diode ofFIG. 3 according to an embodiment of the invention. As shown, the growthcharacteristics include a 0.9 Volt peak at about 515.5 nanometers. Asalso shown, the micro-fluorescence image at 500× is generally moderateto good, although it shows certain vertical lines related to defects,which are generally undesirable. As also shown are electroluminescencedata, which are good, and photoluminescence data, which are goodaccording to a specific embodiment.

FIG. 5 is an illustration of micro-fluorescence defect density formultiple laser diode structures according to an embodiment of theinvention. As shown are (1) a base laser diode structure; (2) base laserdiode structure with high indium content and/or thick InGaN regionsbelow the MQW; and (3) base laser diode structure with high indiumcontent and/or thick inGaN regions below the MQW and a strain controlregion. As an example, the base line diode structure may be illustratedby way of FIG. 3 . As shown, the strain control region provides forlower defect density and facilitates integration and use of the highindium content and/or thick inGaN regions below the MQW. The high indiumcontent and/or thick InGaN regions lead to improved laser diodecharacteristics based upon optical confinement or other purposes, whilethe strain control region causes improved characteristics from the MQW.Such improved characteristics include lower defect density according toa preferred embodiment.

FIG. 6 is a flow diagram of a method of tuning an active region for adesired strain characteristic according to an embodiment of theinvention. In a specific embodiment, the present method may be outlinedas follows:

-   -   1. Provide a gallium and nitrogen containing substrate into a        reaction chamber for growth;    -   2. Deposit an n-type cladding regions overlying the substrate        using a growth method;    -   3. Deposit a high indium content or thick InGaN or low Al        content InAlGaN regions in desirable compositions and doping for        desirable waveguiding and electrical characteristics;    -   4. Deposit higher bandgap strain control regions with desired        thickness and doping levels overlying the high indium content        InGaN or InAlGaN regions;    -   5. Deposit MQW active regions overlying the strain control        regions;    -   6. Optionally, deposit SCH regions overlying the MQW regions;    -   7. Optionally, deposit electron blocking regions overlying the        SCH regions or MQW;    -   8. Deposit p-type cladding regions overlying the electron        blocking regions;    -   9. Deposit p-type contact regions overlying the p-type cladding        regions;    -   10. Remove completed substrate from chamber;    -   11. Perform remaining processes to form laser diode devices; and    -   12. Perform other steps, as desired.

FIG. 7 is an illustration of a method of providing waveguidecharacteristics for laser diode devices according to embodiments of theinvention. As shown, the graphical illustration shows opticalconfinement for within p-type regions such as the p-cladding in apositive direction and negative direction. The illustration also showsan intersecting axis of optical confinement for MQW in a positivedirection and a negative direction. A baseline starting point isprovided at the intersection or origin, which represents the confinementcharacteristics for a baseline laser design without inclusion of thehigh indium content and/or thick InGaN (Super SCH) region or straincontrol region. Also shown are a most preferred modification and a leastpreferred modification. In a preferred embodiment, optical confinementis in the negative p-type region direction and in the positive MQWdirection relative to the baseline design at the origin. Other quadrantsinclude those for improvements such as reduced optical confinement inthe p-type regions and reduced confinement in the MQW region orincreased optical confinement in the MQW and increased opticalconfinement in the p-type regions, although not most preferable. In apreferred embodiment, the active region is configured with a straincontrol region to facilitate integration of a high indium content regionor thick indium content region, which achieves desirable confinementcharacteristics of the optical mode.

FIG. 8 is an illustration of photoluminescence peak intensity formultiple laser diode structures according to an embodiment of theinvention. As shown are (1) a base laser diode structure; (2) base laserdiode structure with high indium content and/or thick InGaN regionsbelow the MQW; and (3) base laser diode structure with high indiumcontent and/or thick inGaN regions below the MQW and a strain controlregion. As an example, the base line diode structure may be illustratedby way of FIG. 3 . As shown, the strain control region provides forhigher photoluminescence while achieving high indium content and/orthick inGaN regions below the MQW, which are generally desirable. Thatis, the strain control regions below the MQW and above the high indiumcontent and/or thick InGaN layer causes improved characteristics fromthe MQW. Such characteristics include higher photoluminescence accordingto a preferred embodiment.

FIG. 9 is an illustration of electroluminescence power for multiplelaser diode structures according to an embodiment of the invention. Asshown are (1) a base laser diode structure; (2) base laser diodestructure with high indium content and/or thick InGaN regions below theMQW; and (3) base laser diode structure with high indium content and/orthick inGaN regions below the MQW and a strain control region. As anexample, the base line diode structure may be illustrated by way of FIG.3 . As shown, the strain control region provides for higherelectroluminescence power while achieving high indium content and/orthick inGaN regions below the MQW, which are generally desirable. Thatis, the strain control region below the MQW causes improvedcharacteristics from the MQW. Such characteristics include higherelectroluminescence according to a preferred embodiment.

FIG. 10 is an example of a simulation of the refractive index and modeprofile for a green laser diode structure according to an embodiment ofthe invention with the inclusion of the high indium content and/or thickInGaN (Super SCH) region and the strain control region. As shown, avertical axis illustrates a refractive index plotted against a waveguideposition for an improved laser diode device, which will be explained inmore detail below. The device has a gallium and nitrogen containingsubstrate comprising a surface region in a specific embodiment. Thesubstrate is preferably GaN or other suitable material. In a specificembodiment, the surface region includes an InGaN region, which may ormay not be partially relaxed. Overlying the InGaN region is a straincontrol region. In a specific embodiment, the strain control region ismade of GaN. Also, the strain control region is a higher bandgapmaterial such as GaN or AlGaN. As also shown, the device includes ann-type SCH region, which is overlying the GaN. In a specific embodiment,the n-type SCH region comprises InGaN. Overlying the SCH are a pluralityof quantum well regions having an InGaN/GaN alternating structure. In aspecific embodiment, the device also has an upper guide or SCH, whichcan be either GaN or InGaN. The device also has an electron blockingregion, such as those made by AlGaN, AlInGaN or other suitable materialssuch as AlInN. In a specific embodiment, the device has an overlyingp-type cladding region, such as GaN, which is doped. Further details ofgrowth characteristic can be found throughout the present specificationand more particularly below. Further details of the present activeregion can be found below.

The present device provides for selected optical characteristics. Thatis, the device is characterized by a 51% reduction in optical modeconfinement within the pGaN region for reduced loss, which ispreferable. Additionally, the device is characterized by a 13% reductionin an optical mode confinement within the multi-quantum well regions,which will reduce the modal gain, which is not preferable.

The device is provided with one or more of the following epitaxiallygrown elements, but is not limiting.

-   -   an n-cladding layer(s);    -   an InGaN region comprised of an indium content of 10% by weight        and a thickness of about 100 nanometers, but can range from        about 60 nm to about 150 nm and indium content from about 8% to        about 15% and could be others.    -   a higher bandgap region overlying the InGaN region, the higher        bandgap region configured as a strain control region;    -   an SCH region overlying the higher bandgap region;    -   multiple quantum well active region layers comprised of five        3.0-5.5.0 nm InGaN quantum wells separated by six 1.5-10.0 nm        GaN barriers;    -   a p-side SCH layer comprised of InGaN with molar a fraction of        indium of between 1% and 10% and a thickness from 15 nm to 100        nm    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 10        nm to 15 nm and doped with Mg.    -   a p-GaN cladding layer with a thickness from 400 nm to 1000 nm        with Mg doping level of 5E17 cm-3 to 3E19 cm-3    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 5E19 cm-3 to 1E21 cm-3        In a specific embodiment, the laser device is fabricated on a        {20-21} substrate.

FIG. 11 is an example of growth characteristics for the laser diode ofFIG. 10 according to an embodiment of the invention. As shown, thegrowth characteristics include a 0.82 Volt peak at about 519.6nanometers. As also shown, the defect structure observed in themicro-fluorescence image at 500× is generally good to moderate, whichhas been achieved using a combination of a thick InGaN region of about100 nm at about 10% indium content and a higher bandgap material for astrain control region.

FIG. 12 is a transmission electron microscope image for the laser diodeof FIG. 10 according to an embodiment of the invention. As shown, theimages show no observable defects within the SCH or MQW region, which isdesirable. Certain defects, however, can be seen between the n type GaNand thick InGaN material. These defects are believed to be misfitdislocations. It is believed that such defects lead to a reduction instrain within the thick InGaN material causing it to be in a partiallyrelaxed state.

FIG. 13 illustrates microfluorescence of laser devices without straincontrol regions according to embodiments of the invention. The laserdevice is similar to the one in FIG. 10 without the strain controlregions or higher bandgap regions. As shown are micro-fluorescenceimages of (1) a laser diode device with a higher bandgap regionoverlying a partially relaxed inGaN material; and (2) a laser diodedevice without the higher bandgap region, which is highly defected.

FIG. 14 is an example of growth characteristics for a laser diode ofFIG. 13 according to an embodiment of the invention. As shown, thegrowth characteristics include a 0.3 Volt peak at about 512.4nanometers, which is a lower peak voltage than preferred embodiments. Asalso shown, the micro-fluorescence image at 500× is generally poor as itshows a very high defect density, which has been caused using a thickInGaN region of about 100 nmat about 10% indium content and without thehigher bandgap material or strain control region.

FIGS. 15A and 15B are transmission electron microscope images ofcross-sections of laser diodes without strain control regions accordingto embodiments of the invention. As shown, a substantial defect densitycan be seen between the n type GaN substrate and thick InGaN material,which indicates that the InGaN layer is substantially more relaxed thatthe structure in FIG. 12 that includes the strain control region. Theimages also show observable defects within the MQW region, which areundesirable.

FIG. 16 is an example of a simulation of the refractive index and modeprofile for a green laser diode structure according to an alternativeembodiment of the invention with the inclusion of the high indiumcontent and/or thick InGaN (Super SCH) region and the strain controlregion. As shown, a vertical axis illustrates a refractive index plottedagainst a waveguide position for an improved laser diode device, whichwill be explained in more detail below. The device has a gallium andnitrogen containing substrate comprising a surface region in a specificembodiment. The substrate is preferably GaN or other suitable material.In a specific embodiment, the surface region includes an InGaN region,which may or may not be partially relaxed. Overlying the InGaN region isa strain control region. In a specific embodiment, the strain controlregion is made of GaN. Also, the strain control region is a higherbandgap material such as GaN. As also shown, the device includes ann-type SCH region, which is overlying the GaN. In a specific embodiment,the n-type SCH region comprises InGaN. Overlying the SCH are a pluralityof quantum well regions having an InGaN/GaN alternating structure. In aspecific embodiment, the device also has an upper guide or SCH, whichcan be either GaN or InGaN. The device also has an electron blockingregion, such as those made by AlGaB, AlInN, AlInGaN or other suitablematerials. In a specific embodiment, the device has an overlying p-typecladding region, such as GaN, which is doped.

The present device provides for selected optical characteristics. Thatis, the device is characterized by a 54% reduction in optical modeconfinement within the pGaN region, which is preferable to reduce modallosses in the laser diode. Additionally, the device is characterized bya 23% reduction in an optical mode confinement within the multi-quantumwell regions, which is not preferable as it will reduce the modal gainof the laser diode.

The device is provided with one or more of the following epitaxiallygrown elements, but is not limiting.

-   -   an n-cladding region;    -   an InGaN region comprised of an indium content of 6% by atomic        percent and a thickness of about 200 nanometers, but can range        from about 150 nm to about 350 nm and indium content from about        4% to about 8% and could be others.    -   a higher bandgap region overlying the InGaN region, the higher        bandgap region configured as a strain control region and has a        thickness of about 10-50 nanometers;    -   an SCH region overlying the higher bandgap region;    -   multiple quantum well active region layers comprised of five        3.0-5.5.0 nm InGaN quantum wells separated by six 1.5-10.0 nm        GaN barriers;    -   a p-side SCH layer comprised of InGaN with molar a fraction of        indium of between 1% and 10% and a thickness from 15 nm to 100        nm    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 10        nm to 15 nm and doped with Mg.    -   a p-GaN cladding layer with a thickness from 400 nm to 1000 nm        with Mg doping level of 5E17 cm-3 to 3E19 cm-3    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 5E19 cm-3 to 1E21 cm-3

The laser device is fabricated on a {20-21} substrate.

FIG. 17 is an example of growth characteristics for the laser diode ofFIG. 16 according to an alternative embodiment of the invention. Asshown, the growth characteristics include a 1.1 Volt peak at about 514.5nanometers. As also shown, the micro-fluorescence image at 500× isgenerally good, which has been achieved using a combination of a thickInGaN region of about 200 nmat about 6% indium content and a higherbandgap material or strain control region ranging in thickness fromabout 10 to 50 nanometers.

FIG. 18 is an example of a simulation of the refractive index andoptical mode profile of a green laser diode structure according to analternative embodiment of the invention with the inclusion of the highindium content and/or thick InGaN (Super SCH) region and the straincontrol region. As shown, a vertical axis illustrates a refractive indexplotted against a waveguide position for an improved laser diode device,which will be explained in more detail below. The device has a galliumand nitrogen containing substrate comprising a surface region in aspecific embodiment. The substrate is preferably GaN or other suitablematerial. In a specific embodiment, the surface region includes anInGaNregion, which may or may not be partially relaxed. Overlying the InGaNregion is a strain control region. In a specific embodiment, the straincontrol region is made of GaN. Also, the strain control region is ahigher bandgap material such as GaN or AlGaN. Overlying the straincontrol region are a plurality of quantum well regions having anInGaN/GaN alternating structure. In a specific embodiment, the devicealso has an upper guide or SCH, which can be either GaN or InGaN. Thedevice also has an electron blocking region, such as those made byAlGaN, AlInGaN, or AlInN or other suitable materials. In a specificembodiment, the device has an overlying p-type cladding region, such asGaN, which is doped.

The present device provides for selected optical characteristics. Thatis, the device is characterized by a 3% increase in an optical modeconfinement within the multi-quantum well regions, which is preferableas it will increase the modal gain. Additionally, the device ischaracterized by a 37% reduction in optical mode confinement within thepGaN region, which is preferable as it will reduce the modal loss.

The device is provided with one or more of the following epitaxiallygrown elements, but is not limiting.

-   -   an n-cladding layer(s);    -   an InGaN region comprised of an indium content of 6% by atomic        percent and a thickness of about 200 nanometers, but can range        from about 150 nm to about 350 nm in thickness and about 4% to        about 8% indium content.    -   a higher bandgap region overlying the InGaN region, the higher        bandgap region configured as a strain control region and has a        thickness of about 10-50 nanometers;    -   multiple quantum well active region layers comprised of five        3.0-5.5.0 nm InGaN quantum wells separated by six 1.5-10.0 nm        GaN barriers;    -   a p-side SCH layer comprised of InGaN with molar a fraction of        indium of between 1% and 10% and a thickness from 15 nm to 100        nm    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 10        nm to 15 nm and doped with Mg.    -   a p-GaN cladding layer with a thickness from 400 nm to 1000 nm        with Mg doping level of 5E17 cm-3 to 3E19 cm-3    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 5E19 cm-3 to 1E21 cm-3

In a specific embodiment, the laser device is fabricated on a {20-21}substrate.

FIG. 19 is an example of growth characteristics for the laser diode ofFIG. 18 according to an alternative embodiment of the invention. Asshown, the growth characteristics include a 0.83 Volt peak at about512.4 nanometers. As also shown, the micro-fluorescence image at 500× isgenerally good with substantially few defects, which has been achievedusing a combination of a thick InGaN region of about 200 nmat about 6%indium content and a higher bandgap material or strain control regionranging in thickness from about 10 to 50 nanometers.

FIG. 20 is an example of a simulation of the refractive index andoptical mode profile of a green laser diode structure according to analternative embodiment of the invention with the inclusion of the highindium content and/or thick InGaN (Super SCH) region and the straincontrol region. As shown, a vertical axis illustrates a refractive indexplotted against a waveguide position for an improved laser diode device,which will be explained in more detail below. The device has a galliumand nitrogen containing substrate comprising a surface region in aspecific embodiment. The substrate is preferably GaN or other suitablematerial. In a specific embodiment, the surface region includes anInGaNregion which may or may not be partially relaxed. Overlying the InGaNregion is a strain control region. In a specific embodiment, the straincontrol region is made of GaN. Also, the strain control region is ahigher bandgap material such as GaN or AlGaN. Overlying the straincontrol region are a plurality of quantum well regions having anInGaN/GaN alternating structure. In a specific embodiment, the devicealso has an upper guide or SCH, which can be either GaN or InGaN. Thedevice also has an electron blocking region, such as those made byAlGaN, AlInGaN, AlInN or other suitable materials. In a specificembodiment, the device has an overlying p-type cladding region, such asGaN, which is doped.

The device provides for a 12% increase in an optical mode confinementwithin the multi-quantum well regions, which is preferable as it willincrease the modal gain of the laser diode. Additionally, the device ischaracterized by a 35% reduction in optical mode confinement within thepGaN region, which is preferable as it will reduce the modal loss of thelaser diode.

The device is provided with one or more of the following epitaxiallygrown elements, but is not limiting.

-   -   an n-cladding layer(s);    -   an InGaN region comprised of an indium content of 15% by atomic        percent and a thickness of about 60 nanometers, but can range        from about 30 nm to about 80 nm in thickness and about 10% to        about 17% indium content.    -   a higher bandgap region overlying the InGaN region, the higher        bandgap region configured as a strain control region and has a        thickness of about 10-50 nanometers;    -   multiple quantum well active region layers comprised of five        3.0-5.5.0 nm InGaN quantum wells separated by six 1.5-10.0 nm        GaN barriers;    -   a p-side SCH layer comprised of InGaN with molar a fraction of        indium of between 1% and 10% and a thickness from 15 nm to 100        nm    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 10        nm to 15 nm and doped with Mg.    -   a p-GaN cladding layer with a thickness from 300 nm to 1000 nm        with Mg doping level of 5E17 cm-3 to 3E19 cm-3    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 5E19 cm-3 to 1E21 cm-3

In a specific embodiment, the laser device is fabricated on a {20-21}substrate.

FIG. 21 is an example of growth characteristics for the laser diode ofFIG. 18 according to an alternative embodiment of the invention. Asshown, the growth characteristics include a 0.4 Volt peak at about 519.6nanometers. As also shown, the micro-fluorescence image at 500× isgenerally good, which has been achieved using a combination of a thickInGaN region of about 60 nm at about 15% indium content and a higherbandgap material or strain control region ranging in thickness fromabout 10 to 50 nanometers.

FIG. 22A is an example of a simulation of the refractive index andoptical mode profile of a green laser diode structure with high indiumcontent InGaN region above and below the MQW of a laser diode accordingto an alternative embodiment of the invention with the inclusion of thehigh indium content and/or thick InGaN (Super SCH) region(s) and thestrain control region(s). As shown, the MQW is configured between a pairof the strain control regions and respective pair of Super SCH regionsor high indium content and/or thick InGaN regions. In this example, thehigh indium content and/or thick InGaN layer is about 60 nm and has a12% indium content, although there can be variations. The present deviceprovides a 23% increase in an optical mode confinement within themulti-quantum well regions. Additionally, the device is characterized bya 54% reduction in optical mode confinement within the pGaN region. Thehigher bandgap strain control layer is about 10 to 50 nm thick, and iscomposed of GaN. In other examples, each of the high indium contentand/or thick InGaN layers may be configured differently with substantialor slight variations.

FIG. 22B is an example of a simulation of the refractive index andoptical mode profile of a green laser diode structure with a daisy chainof high indium content and strain control regions configured to tune alattice constant within an active region of a laser diode according toan alternative embodiment of the invention. As shown, the deviceincludes a plurality of high indium content and/or thick InGaN layersintegrated with a plurality of high bandgap strain control regionsaccording to this example. As shown, the device includes a first, asecond, and a third high indium content and/or thick InGaN layer. Afirst strain control region is provided spatially between the first andsecond indium content layers. A second stain control region is providedspatially between the second and third indium content layers. A thirdstrain control region is provided spatially between the third indiumcontent layer and multiquantum well region, as shown. In otherembodiments, the optical device can include N indium content layers,where N is an integer greater than three (3) and also include M straincontrol regions, where M is an integer greater than three (3), althoughM and N may not be equal in some cases.

In this example, the high indium content and/or thick InGaN layer isabout 100 nm and has a 10% indium content, although there can bevariations. The higher bandgap strain control layer is about 8 to 50 nmthick, and is composed of GaN, but could be others. In other examples,each of the high indium content and/or thick InGaN layers may beconfigured differently with substantial or slight variations.

The method forms via growth multiple high indium content and/or thickInGaN layers followed by stain control regions. It is believed a latticeconstant can be altered continuously and integrally from the first staincontrol region to the second strain control region. As an example, thelattice constant in strain control regions near the multiquantum wellare configured and will be larger (similar to InGaN with a higher indiumcomposition), which should enable growth of higher indium contentmultiquantum wells. Such higher indium content multiquantum wells canlead to emission of electromagnetic radiation in wavelength ranges inyellow and even red regimes or could lead to improved efficiency in thered, green, or yellow regimes. In such embodiments, cladding regions andassociated barriers are comprised of InGaN (since GaN would be strainedto the new lattice constant, and would not form effectively).

FIG. 22C is an example of a simulation of the refractive index andoptical mode profile of a green laser diode structure with anintermediate strain control region within a high indium content and/orthick InGaN regions of a laser diode according to an alternativeembodiment of the invention. As shown, the device includes a pluralityof high indium content and/or thick InGaN layers integrated with aplurality of high bandgap strain control regions according to thisexample. As shown, the device includes a first and a second high indiumcontent and/or thick InGaN layer. A first strain control region isprovided spatially between the first and second indium content layers. Asecond strain control region is provided spatially between the secondindium content layer and multiquantum well region, as shown. That is,other embodiments can include any combination of intermediary straincontrol layers, including multiple strain control layers integrallydisposed with high indium content and/or thick InGaN layers.

In this example, the high indium content and/or thick InGaN layer isabout 30 nm and has a 15% indium content, although there can bevariations. The higher bandgap strain control layer is about 3 to 30 nmthick for the intermediate layer and about 10 to 50 nm for the uppermoststrain control layer, and is composed of GaN. In this example the n-SCHis removed from between the high indium content and/or thick InGaN layerand the higher bandgap layer. The present device provides a 8% increasein an optical mode confinement within the multi-quantum well regions.Additionally, the device is characterized by a 35% reduction in opticalmode confinement within the pGaN region. In other examples, each of thehigh indium content and/or thick InGaN layers may be configureddifferently with substantial or slight variations.

FIG. 22D is an example of the refractive index and optical mode profileof a green laser diode structure employing multiple intermediate straincontrol regions within a high indium content and/or thick InGaN regionsaccording to an alternative embodiment of the invention. As shown, thedevice includes a plurality of high indium content and/or thick InGaNlayers integrated with a plurality of high bandgap strain controlregions.

In this example, the high indium content and/or thick InGaN layer isabout 30 nm and has a 15% indium content, although there can bevariations. The higher bandgap strain control layer is about 3 to 30 nmthick for the intermediate layer and about 10 to 50 nm for the uppermoststrain control layer, and is composed of GaN. The present deviceprovides a 10% increase in an optical mode confinement within themulti-quantum well regions. Additionally, the device is characterized bya 35% reduction in optical mode confinement within the pGaN region. Inthis example the n-SCH is removed from between the high indium contentand/or thick InGaN layer and the higher bandgap layer. In otherexamples, each of the high indium content and/or thick InGaN layers maybe configured differently with substantial or slight variations.

The present method and structure provide for a selective configurationof multiple strain control regions coupled to multiple high indiumand/or thick InGaN regions. Each of the regions can be selectively tunedto increase a lattice constant from a GaN substrate region to a quantumwell region. By way of increasing the lattice constant, indium ispreferably added into a gallium and nitrogen containing material in themulti-quantum well region, which now has less strain leading to fewerdefects and degradation.

The invention provides an optical device having multiple high indiumand/or thick InGaN regions. As an example, such device includes agallium and nitrogen containing substrate comprising a surface regionoriented in either a semipolar or non-polar configuration. The devicealso has a first gallium and nitrogen containing material comprisingInGaN overlying the surface region. The device has a first straincontrol region overlying the first gallium and nitrogen containingmaterial and a second gallium and nitrogen containing materialcomprising InGaN overlying the surface region. The device also has asecond strain control region overlying the first gallium and nitrogencontaining material and a plurality of quantum well regions overlyingthe strain control region. In a specific embodiment, the device furthercomprising an nth strain control region, where n is an integer greaterthan two (2), three, four, five, six, and others. Each of the straincontrol regions is configured with at least one high indium indiumand/or thick InGaN region or a pair of such regions. Each of the straincontrol regions has a lattice constant which is larger from the GaNsubstrate toward the multi-quantum well region. The lattice constantsincrease from a first lattice constant, second lattice constant . . . toan nth lattice constant, which helps facilitates the formation of amultiquantum well region for longer wavelength emissions, e.g., red,yellow. FIG. 23 is a simplified example of a simulation of therefractive index and optical mode profile of a green laser diodestructure with a high indium content InGaN layer that causes the totalstructure to exceed a total strain budget according to an embodiment ofthe invention. In another example, the present device exceeds a stainbudget, which leads to undesirable characteristics. The device includesa similar structure, however, the indium content of the 100 nm partiallyrelaxed InGaN region is 15% and greater. The present device provides a32% reduction in an optical mode confinement within the multi-quantumwell regions. Additionally, the device is characterized by a 72%reduction in optical mode confinement within the pGaN region.

FIG. 24 is an example of growth characteristics for a laser diode ofFIG. 23 according to the alternative embodiment of the invention. Asshown, the growth characteristics include a 0.56 Volt peak at about518.6 nanometers. As also shown, the micro-fluorescence image at 500× isgenerally different or hatched, which has been caused using acombination of a thick InGaN region having a high indium content, whichis beyond some threshold, and a higher bandgap material or straincontrol region ranging in thickness from about 10 to 50 nanometers.

FIG. 25 includes transmission electron microscope images of the laserdiode of FIG. 23 according to the alternative embodiment of theinvention. As shown, the images show observable defects within the MQWand SCH regions, which are undesirable. Substantial defects can be seenbetween the n type GaN layer and thick InGaN material.

FIGS. 26 and 27 are illustrations of reciprocal space map (RSM) plots oflaser diode devices according to embodiments of the invention. The GaNsubstrate is characterized by a tilt angle of zero and is configured ona semi-polar plane such as {20-21}, but can have variations,modifications, and alternatives. In the present example, the substrateincludes growth structures similar to those described in the presentspecification. FIG. 26 is for a laser diode device including a growthstructure free from HS-SCH. In this example, the tilt angle of the nSCHto the substrate is 0.15 degrees; the average misfit dislocation spacingis ˜103 nm; the MQW 0^(th) order and nSCH peaks overlap (this nSCH/MQWpeak is not in a straight line with the substrate, so the nSCH/MQW isnot lattice matched with the substrate); the pGaN is likelypartially-relaxed (tensile strain); and it is estimated that there aremisfit dislocations at the nSCH/nGaN and in the vicinity of the pGaN/EBLinterface. FIG. 27 is for a laser diode device including a growthstructure having HS-SCH, which shows that the lattice constant ofoverlying regions are substantially equal and different from the GaNsubstrate. In this example, the tilt angle of the nSCH to the substrateis 0.526 degrees; the tilt angle of the HS-SCH to the substrate is 0.530degrees (about the same as the nSCH); the average misfit dislocationspacing is ˜29 nm; the MQW 0^(th) order and nSCH peaks overlap; theHS-SCH, nSCH, and pGaN are not coherent with respect to the substrate;the tilt angles of the HS-SCH, nSCH peak are significantly larger thanthe regular LD (most likely the nSCH is pseudomorphic with respect tothe partially-relaxed HS-SCH); and the pGaN is likely partially-relaxed(tensile strain). As shown FIGS. 26 and 27 , a tilt angle of the SCH/MQWincreases from 0.15 Degree to 0.53 Degree (causing a difference in tiltangles, e.g., greater than 2×, 3×, 4×) upon adding the HS-SCH, whichcorresponds to an average misfit dislocation spacing changing from 103nm to 29 nm. In a specific embodiment, the in-plane lattice-constantparallel to c-projection <1016> for the HS-SCH is larger than that forthe nSCH (in the FIG. 26 LD structure), which itself is larger than thatfor the underlying GaN substrate. Also, it is clear from the TEM andmicro-fluorescence data that if the strain control layer is omitted, themisfit dislocation density is drastically higher and the materialquality breaks down eliminating the material's suitability for growinghigh quality light emitting regions in this particular laser structure.It is believed, as supported by the RMS plots, that the presentcombination of strain control region and semi-polar oriented substratesleads to relaxation of overlying regions, which yield larger latticeconstants, unlike the conventional devices. One or more of the featuresof the present method and structure are as follows:

1. In a specific embodiment, the present method and structuresubstantially changes the lattice constant, which was unexpected, of thelight emitting region while maintaining good material quality in thelight emitting region when the relaxation layer is introduced followedby the strain control layer. Note: Conventional epitaxial growth onconventional c-plane substrates does not cause a change in in-planelattice constant (i.e., less than 0.1%) and therefore leads to largedislocations and/or breakage of subsequently grown epitaxial regions.

The present method and structure allows for introduction of higherindium content layers in our epitaxial structure to maintain highefficiency light emitting regions for additional design flexibility suchas improved wave guiding in laser diodes.

The method and structure allows for the growth of a relaxation layer andthen grow subsequent layers on top with a different lattice constant.The relaxation layer can be a gallium containing, nitrogen containing,and indium containing region, but may have variations. Depending uponthe embodiment, different epitaxial structures can be provided overlyingthe relaxation layer(s).

Although the above has been described in terms of specific embodiments,there can be other variations, modifications, and alternatives. As anexample, the embodiments above are described in terms of a certain pGaNconfinement. However, the pGaN confinement may be generalized toconfinement of p-type regions, which includes p-type cladding regions.In other examples, the p-type confinement includes pAlGaN. In otherembodiments, the technique can be generalized to any p-type region abovea MQW region and the like.

As used herein, the term GaN substrate is associated with GroupIII-nitride based materials including GaN, InGaN, AlGaN, or other GroupIII containing alloys or compositions that are used as startingmaterials. Such starting materials include polar GaN substrates (i.e.,substrate where the largest area surface is nominally an (h k l) planewherein h=k=0, and 1 is non-zero), non-polar GaN substrates (i.e.,substrate material where the largest area surface is oriented at anangle ranging from about 80-100 degrees from the polar orientationdescribed above towards an (h k l) plane wherein l=0, and at least oneof h and k is non-zero) or semi-polar GaN substrates (i.e., substratematerial where the largest area surface is oriented at an angle rangingfrom about +0.1 to 80 degrees or 110-179.9 degrees from the polarorientation described above towards an (h k l) plane wherein l=0, and atleast one of h and k is non-zero).

As shown, the present device can be enclosed in a suitable package. Suchpackage can include those such as in TO-38 and TO-56 headers. Othersuitable package designs and methods can also exist, such as TO-9 andeven non-standard packaging. The present device can be implemented in aco-packaging configuration such as those described in U.S. ProvisionalApplication No. 61/347,800, commonly assigned, and hereby incorporatedby reference for all purposes.

The present laser device can be provided in a laser display such asthose described in U.S. Ser. No. 12/789,303 filed May 27, 2010, whichclaims priority to U.S. Provisional Nos. 61/182,105 filed May 29, 2009and 61/182,106 filed May 29, 2009, each of which is hereby incorporatedby reference herein.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. As used herein, the term “substrate” can mean the bulk substrateor can include overlying growth structures such as a gallium andnitrogen containing epitaxial region, or functional regions such asn-type GaN, combinations, and the like. Therefore, the above descriptionand illustrations should not be taken as limiting the scope of theinvention which is defined by the appended claims.

What is claimed is:
 1. A laser diode device comprising: a gallium andnitrogen containing substrate having a surface region and a firstin-plane lattice constant; a strained region overlying the surfaceregion, the strained region having a second in-plane lattice constant,the second in-plane lattice constant being smaller than a nativein-plane lattice constant of the strained region; a strain controlregion overlying at least a portion of the strained region, the straincontrol region having a third in-plane lattice constant; and a pluralityof quantum well regions overlying the strained region, each of theplurality of quantum well regions having a fourth in-plane latticeconstant, the fourth in-plane lattice constant being different than thefirst in-plane lattice constant, wherein the third in-plane latticeconstant maintains at least one of the plurality of quantum well regionswithin a predetermined strain state, and the strain control region has ahigher bandgap than the strained region and the plurality of quantumwell regions.
 2. The laser diode device of claim 1 wherein: the strainedregion comprise an interface region between the substrate and the straincontrol region; and the interface region comprises a plurality ofdislocations.
 3. The laser diode device of claim 1 wherein the surfaceregion is configured in a {20-21} semi-polar orientation, or the surfaceregion is configured to be in an off-set of a {20-21} orientation andthe strained region is at least partially relaxed.
 4. The laser diodedevice of claim 1 further comprising: at least one barrier regionsandwiched between a pair of the plurality of quantum well regions; theat least one barrier region comprising GaN, InGaN, AlGaN, or AlInGaN;and the at least one barrier region ranges in thickness from 1.5 nm to12 nm.
 5. The laser diode device of claim 1 wherein: the strained regioncomprises a single layer of InGaN; the single layer of InGaN has athickness ranging from 20 to 80 nm with 2 to 20% InN content; the singlelayer of InGaN is overlaid with the strain control region comprised ofGaN or AlGaN; and the strain control region has a thickness ranging from2-20 nm with 2 to 40% AlN content.
 6. The laser diode device of claim 1wherein: the strained region comprises multiple layers of GaN, AlN,AlInN, AlGaInN, or InGaN; each of the multiple layers has a thicknessranging from 10 to 50 nm with 2 to 25% InN content; each of the multiplelayers are separated by a layer of the strain control region comprisedof AlGaN; and the strain control layers have thickness ranging from 2-20nm with 2 to 40% AlN content.
 7. The laser diode device of claim 1wherein: the strained region comprises multiple strained layers ofInGaN; the InGaN layers have a thickness ranging from 10 to 50 nm with 2to 25% InN content; the InGaN layers are separated by a layer of thestrain control region comprised of GaN; the thickness of the strainedlayers is equal or decreases with each subsequent layer; and thecomposition of strained layers is equal or increases in InN with eachsubsequent layer.
 8. A laser display apparatus comprising: a laser diodedevice, the laser diode device comprising: a gallium and nitrogencontaining substrate having a surface region and a first in-planelattice constant; a strained region overlying the surface region, thestrained region having a second in-plane lattice constant, the secondin-plane lattice constant being smaller than a native in-plane latticeconstant of the strained region; a strain control region overlying atleast a portion of the strained region, the strain control region havinga third in-plane lattice constant; and a plurality of quantum wellregions overlying the strained region, each of the plurality of quantumwell regions having a fourth in-plane lattice constant, the fourthin-plane lattice constant being different than the first in-planelattice constant, wherein the third in-plane lattice constant maintainsat least one of the plurality of quantum well regions within apredetermined strain state, and the strain control region has a higherbandgap than the strained region and the plurality of quantum wellregions.
 9. The laser display apparatus of claim 8 wherein the surfaceregion is configured in a {20-21} semi-polar orientation, or the surfaceregion is configured to be in an off-set of a {20-21} orientation andthe strained region is at least partially relaxed.
 10. The laser displayapparatus of claim 8 further comprising: at least one barrier regionsandwiched between a pair of the plurality of quantum well regions; theat least one barrier region comprising GaN, InGaN, AlGaN, or AlInGaN;and the at least one barrier region ranges in thickness from 1.5 nm to12 nm.
 11. The laser display apparatus of claim 8 wherein: the strainedregion comprises a single layer of InGaN; the single layer of InGaN hasa thickness ranging from 20 to 80 nm with 2 to 20% InN content; thesingle layer of InGaN is overlaid with the strain control regioncomprised of GaN or AlGaN; and the strain control region has a thicknessranging from 2-20 nm with 2 to 40% AlN content.
 12. The laser displayapparatus of claim 8 wherein: the strained region comprises multiplelayers of GaN, AlN, AlInN, AlGaInN, or InGaN; each of the multiplelayers has a thickness ranging from 10 to 50 nm with 2 to 25% InNcontent; each of the multiple layers are separated by a layer of thestrain control region comprised of AlGaN; and the strain control layershave thickness ranging from 2-20 nm with 2 to 40% AlN content.
 13. Thelaser display apparatus of claim 8 wherein: the strained regioncomprises multiple strained layers of InGaN; the InGaN layers have athickness ranging from 10 to 50 nm with 2 to 25% InN content; the InGaNlayers are separated by a layer of the strain control region comprisedof GaN; the thickness of the strained layers is equal or decreases witheach subsequent layer; and the composition of strained layers is equalor increases in InN with each subsequent layer.
 14. A system comprising:a laser display, and a laser diode device configured to provide lightfor the laser display, the laser diode device comprising: a gallium andnitrogen containing substrate having a surface region and a firstin-plane lattice constant; a strained region overlying the surfaceregion of the gallium and nitrogen containing substrate, the strainedregion having a second in-plane lattice constant, the second in-planelattice constant being smaller than a native in-plane lattice constantof the strained region; at least one strain control region overlying atleast a portion of the strained region, the at least one strain controlregion having a third in-plane lattice constant; and a plurality ofquantum well regions overlying the at least one strain control region,each of the plurality of quantum well regions having a fourth in-planelattice constant, the fourth in-plane lattice constant being differentthan the first in-plane lattice constant, wherein the third in-planelattice constant maintains at least one of the plurality of quantum wellregions within a predetermined strain state, and the at least one straincontrol region has a higher bandgap than the strained region and theplurality of quantum well regions.
 15. The system of claim 14 whereinthe second in-plane lattice constant is larger than the first in-planelattice constant.
 16. The system of claim 14 wherein the third in-planelattice constant is substantially equivalent to the second in-planelattice constant.
 17. The system of claim 14 wherein the fourth in-planelattice constant is substantially equivalent to the second in-planelattice constant.
 18. The system of claim 14 wherein the fourth in-planelattice constant is substantially equivalent to the third in-planelattice constant.
 19. The system of claim 14 wherein the strained regionprovides optical confinement for the laser diode device.
 20. The systemof claim 14 wherein the strained region comprises a plurality ofstrained regions, and the at least one strain control region comprises aplurality of strain control regions, and wherein adjacent ones of theplurality of strained regions are separated by one of the plurality ofstrain control regions.